With reference being initially made to FIGS. 5-7 of the drawings, a strap-binding operation of the type noted hereinabove is conventionally carried out by means of a multi-functional binding head 1 which is vertically movable with respect to the frame of the binding machine. As more particularly shown in FIG. 5, the strap binding process or operation, as performed by means of such conventional strap-binding apparatus, comprises the steps of feeding a band-like binding strap 3 in a forward feeding direction f by means of forward rotation of reversible-drive rollers 2 such that the binding strap 3 encircles an article 4 to be bound. Upon completion of, in effect, a closed loop around the article 4, the leading end portion 3a of the binding strap 3 is gripped by means of a gripper apparatus or unit, not shown, disposed within the binding head 1, and subsequently, the rotational drive of the drive rollers 2 is reversed such that the trailing end portion 3b of the binding strap 3 is retracted in the reverse direction tt such that the binding strap 3 is preliminarily tightened about the article 4 being bound. Subsequently, the reverse drive of the rollers 2 is continued whereby the binding strap 3 is tightened about the article 4 with a high degree of tension, and while the strap 3 is disposed in such a tensioned state, the overlapped leading and trailing end portions 3a and 3b of the binding strap 3 are bonded together at a location which is disposed downstream of the gripping station at which the gripping unit is disposed, by means of a seal fitment or crimped ferrule, or the like.
Continuing further, after the overlapping strap portions 3a and 3b have been bonded to each other, the bonded trailing end portion 3b of the strap 3 is severed and separated from the residual supply portion 3c of the binding strap 3. In performance of the bonding operation, crimping means, not shown, operatively cooperate with an underlay or undersurface support plate or block, also not shown, which is interposed between the article 4 being bound and the overlapped portions 3a and 3b of the binding strap 3. Consequently, upon completion of the bonding operation, the underlay or support block is transversely removed from its position between the bound article 4 and the overlapped portions 3a and 3b of the binding strap 3 whereby the bonded strap 3 disposed about the bound article 4 is loosened to a predetermined degree corresponding to the volume of the gap space vacated by means of the removed underlay or support block. However, in view of the highly tensioned state existing within the bound binding strap, and the inherent resiliency developed therein, such looseness or slack developed within the bound binding strap is immediately absorbed so that the tensioned bound state is in fact sufficiently maintained.
Reference now being made to FIG. 6 of the drawings, there is shown the drive roller system 2 which is disposed within the conventional binding head 1, and FIG. 7 specifically illustrates, in a schematic mode, the interacting dynamics developed between the traction roller 2T and the back-up roller 2B. More particularly, the traction roller or traction wheel 2T is provided with a knurled-type groover peripheral surface, and the back-up wheel or roller 2B is provided with a smooth peripheral surface. The binding strap 3 is of course interposed between the traction and back-up wheels or rollers 2T and 2B so as to be disposed within the bight or nip portion thereof within a predetermined amount of pressurized force developed therebetween.
According to this aforenoted conventional arrangement, the back-up wheel 2B is rotatably supported in such a manner that the same rotates about an axis b at a predeterminedly fixed position with respect to the frame portion of the binding head 1, while the traction wheel or roller 2T is rotatably incorporated within an eccentric mounting mechanism such that the traction wheel or roller 2T can approach the back-up wheel 2B in order to cooperate therewith in compressing the binding strap 3 therebetween. More particularly, the traction wheel 2T is eccentrically mounted upon an eccentric housing 5 by means of an eccentric shaft having an axis t about which traction wheel 2T rotates, and wherein the axis t of the traction wheel 2T and the eccentric shaft thereof is displaced by means of a a radial distance x from the pivotal base axis X of the eccentric housing 5. The structural arrangement is such that when the eccentric housing 5, which is operatively connected to a rotary motor 6 and a reduction gear drive 7 as shown in FIG. 6, is pivoted around the base axis X, the axis t is eccentrically moved with respect to axis X such that the traction wheel 2T can approach the back-up wheel 2B.
It is further appreciated that a spring 8 is interposed between the eccentric housing 5 and the frame of the binding head 1 such that the traction wheel 2T is always biased in the direction of engaging the back-up wheel 2B. In this manner, the spring 8 enables the driving wheel or driving roller system to feed or retract the binding strap 3 with a relatively small amount of pressure developed between the traction wheel 2T and the back-up wheel 2B. However, during the tightening, and particularly during the tensioning, phase of the binding operation, it is required that the binding strap 3 be strongly tensioned by means of a strong contact pressurized force and a strong traction torque developed by means of the traction wheel 2T. Such strong tensioning of the binding strap 3 is able to be achieved in the following manner. Upon completion of the initial strap tightening operation, the binding strap 3 encounters increased resistance to continued retraction in the tt direction, and when the traction wheel 2T is in fact operating in its reverse drive, low-speed, high-torque mode, the traction wheel 2T tends to be moved somewhat in the reverse direction tt as shown in FIG. 7. Accordingly, the traction wheel 2T will move, in effect, in a wedging direction in which the wedge angle .alpha., which is formed by, and subtends, the radial displacement x defined between the axes X and t of the eccentric housing 5 and the traction wheel 2T as the traction wheel 2T comes into contact with the back-up wheel 2B, will tend to be reduced. The wedge angle .alpha. usually has a predetermined value of approximately 5.degree.-6.degree. when the traction wheel 2T is engaged with the back-up wheel 2B, while the entire pivotable range of the eccentric housing 5 and traction wheel 2T is approximately 15.degree.-30.degree.. Accordingly, the pressurizing force developed between both wheels 2T and 2B is increased by means of the aforenoted wedging effect, and this phenomenon, wherein the tension within the strap is increased together with, in response to, or as a function of, the increase in the pressurizing force developed between both traction and back-up wheels 2T and 2B, respectively, is known as self-energization. Such self-energization phenomenon achieves the strong tensioning characteristics within the strapping band, and it is to be appreciated that when the steel band strap 3 has, for example, a width of 0.75-1.25 inches or 19-32 mm, a thickness of approximately 0.9 mm, and a tensile strength of approximately 75-100 kgs/mm.sup.2, the pressing force developed between the traction wheel 2T and the back-up wheel 2B has a magnitude which is several times that of the strap tension.
As may readily be appreciated, the conventional strap-binding apparatus exhibits several drawbacks, problems, and operational disadvantages. As has been noted hereinabove, the binding strap may be forwardly fed or reversely retracted as a result of the development of a relatively small pressurizing force developed between the traction and back-up wheels 2T and 2B, respectively, in view of the disposition or presence of spring 8, and the adjustment of the spring or the resulting force may be readily achieved. For example, during tensioning of the binding strap, the pressurizing force developed between the traction and back-up wheels 2T and 2B, respectively, may be substantially increased when the wedge angle .alpha. is rendered small, and similarly, in reverse, that is, the pressurizing force may be reduced when the wedge angle .alpha. is rendered relatively large, considerable variations in the developed pressurizing force therefore being obtainable as a direct function, in an inverse manner, of the variation of the wedge angle .alpha.. This structural arrangement, however, renders the adjustment quite difficult in view of the fact that optimum conditions under which the binding strap is tensioned without the development of slippage by means of the traction wheel 2T can vary with the type and thickness of the binding strap 3 employed. It is therefore practically impossible that predetermined setting conditions or adjustments of the wedge angle .alpha. will properly accommodate all types and thicknesses of binding straps to be used in such binding operations. If in fact the adjustment and tensioning conditions are not in fact properly set or predetermined, the binding strap may experience slippage. Such an operational occurrence not only fails to properly or smoothly tighten and tension the binding strap, but such also results in an effective loss of motor output. In a similar but reverse manner, if the pressurizing force is excessive, such a situation or condition may cause the grooves defined within the peripheral surface of the traction wheel 2T to bite into or gouge the binding strap, thereby imparting scar marks thereto. Such conditions may subsequently lead to the likelihood that during the final tensioning phase of the binding operation, the strap may tear or experience partial disintegration at such scar mark sites. Such conditions can of course lead to defective binding states.
Still further, it is also to be appreciated that in view of the eccentric mounting of the housing 5 having the drive system and traction wheel 2T operatively associated therewith, the housing 5 is necessarily large in size, and accordingly, the binding head 1 is necessarily large in size.